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International audience; Invasive species often settle in specific socio-ecological systems, in which the role of human is central. Our study aims to bring a new perspective on a plant declared as a major invasive, gorse, Ulex europaeus, incorporating human factors and the social context in the analysis of each stage of the invasion process. Gorse was highly valued in its area of origin, Europe, which has led to its voluntary introduction in many European colonies to the 19th century. It is now considered invasive in more than 30 countries and on all continents. The site chosen is the island of Reunion, whose characteristics make it a laboratory for the study: the space is circumscribed, human presence is recent, and archives are available on almost the entire history of colonization. The collected materials are composed of archive extracts, bibliographic documents, semi-structured interviews, maps, and biological data. They were systematically analyzed by time and space. The spatiotemporal dynamics of gorse has been finely traced since its introduction, in conjunction with the ecology of the plant, the characteristics of natural environments, and successive changes in policies and economic status of spaces occupied by the plant. The biological invasion gorse appears as the result of complex processes binder in a seamless web interaction between introduced species and natural environment and the history of social, economic and cultural relationships that humans have with their environment.; Les espèces invasives s’établissent souvent dans des systèmes socio-écologiques particuliers, où le rôle des humains est central. Notre étude a pour objectif d’apporter un nouveau regard sur une plante déclarée invasive majeure, l'ajonc d’Europe, Ulex europaeus, en intégrant les facteurs humains et le contexte social dans l'analyse de chaque stade du processus d’invasion. L’ajonc a été très valorisé dans sa zone d’origine, l'Europe, ce qui a induit son introduction volontaire dans de nombreuses colonies européennes vers le xixe siècle. Il est aujourd'hui considéré comme envahissant dans plus de 30 pays et réparti sur tous les continents. Le site choisi est l’île de La Réunion ; ses caractéristiques en font un laboratoire d’étude : le milieu est circonscrit, la présence humaine est récente, et les archives sont disponibles sur la quasi-intégralité de l’histoire de la colonisation. Les matériaux collectés sont composés d'extraits d'archives, de documents bibliographiques, d’entretiens semi-directifs, de cartographies, et de données biologiques. Ils ont été analysés de manière systématique, par époque et par espace. La dynamique spatio-temporelle de l’ajonc a été retracée de manière fine depuis son introduction, en liaison à la fois avec l'écologie de la plante, les caractéristiques des milieux naturels et les modifications successives des statuts politiques et économiques des espaces occupés par la plante. L’invasion biologique par l’ajonc dans l’île apparaît comme le résultat de processus complexes liant dans un « tissu sans coutures » l’interaction espèce introduite-milieu naturel et l’histoire des rapports sociaux, économiques et culturels que les humains entretiennent avec leur environnement.

International audience; Phenotypic plasticity may be advantageous for plants to be able to rapidly cope with new and changing environments associated with climate change or during biological invasions. This is especially true for perennial plants, as they may need a longer period to respond genetically to selective pressures than annuals, and also because they are more likely to experience environmental changes during their lifespan. However, few studies have explored the plasticity of the reproductive life history traits of woody perennial species. This study focuses on a woody shrub, Ulex europaeus (common gorse), and on the response of its reproductive traits to one important environmental factor, shading. The study was performed on clones originating from western France (within the native range of this invasive species) and grown for seven years. We compared traits of plants grown in a shade treatment (with two successive shade levels) vs. full natural light. The traits monitored included flowering onset, pod production and seed predation. All traits studied responded to shading, exhibiting various levels of plasticity. In particular, dense shade induced a radical but reversible decrease in flower and pod production, while moderate shade had little effect on reproductive traits. The magnitude of the response to dense shade depended on the genotype, showing a genetically based polymorphism of plasticity. The level of plasticity also showed substantial variations between years, and the effect of environmental variations was cumulative over time. This suggests that plasticity can influence the lifetime fitness of U. Europaeus and is involved in the capacity of the species to grow under contrasting environmental conditions.

The interactions between plants and their parasites usually involve several species and present high level of variation in space and time. According to the geographic mosaic theory of coevolution, this may lead to population differentiation, large polymorphism and local maladaptation. Here we explore whether the temporal and spatial variation of the interaction between gorse (Ulex europaeus) and its seed predators can explain the polymorphism observed within and among populations of its native range. Indeed, gorse individuals present a polymorphism of flowering and fruiting phenology, and large variability for their susceptibility to seed predation. We performed a regular monitoring of five populations localised in Brittany (France) over five consecutive years. We observed the flowering and fruiting phenology of the gorses, and measured pods infestation rates by their two main seed predators, the weevil Exapion ulicis and the moth Cydia succedana. Flowering phenotypes and between year evolution of parasitism rates were conserved from year to year. Parasitism rates by weevils and moths increased over the fruiting period, and were negatively correlated one to another. Long flowering plants were more attacked by weevils, while short-flowering plants were more attacked by moths. However, the majority of the weevil larvae did not develop into adults, either because they were still at an immature stage at pod maturity, or because they were attacked by a parasitoid wasp. Year-to-year variations in the infestation rates by the two seed predators were very high, and depended on the population but not on the microclimatic conditions. These variations can thus explain the maintenance of the within populations polymorphism of gorse phenology and susceptibility to seed predation.

International audience; Reproductive phenology of gorse (Ulex europaeus L., Genisteae, Fabaceae) is unusual in that the onset and duration of flowering vary greatly among individuals within populations: some plants initiate flowering in autumn or winter and continue flowering through spring, others initiate flowering in early spring. To understand the origin of this diversity and its ecological consequences, we investigated flowering phenology of randomly sampled individuals from five different natural populations in Brittany (France). Reproductive success was evaluated for individuals with contrasting flowering patterns, from 16 natural populations. Flower production, pod production, seed production and seed predation were estimated. Plants initiating flowering in spring produced larger numbers of flowers and pods over a shorter period than plants flowering from winter to spring, which produced few flowers and pods at a time but over a longer period. Pod production of longflowering plants did not differ significantly between winter and spring, but their pods were more intensively attacked by seed predators in spring than in winter. We discuss our results in relation to biotic and abiotic parameters. We postulate that long-flowering can be interpreted as a bet-hedging strategy, spreading the risk of pod failure (rotting or freezing) in winter and of seed predation in spring.